Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.67   10.401%   $218.2297   $218.23   $218.25   $218.20  
  Purchase #2 $78.58   8.654%   $85.3803   $85.38   $85.40   $85.40  
  Purchase #3 $161.36   6.815%   $172.3567   $172.36   $172.35   $172.40  
  Purchase #4 $70.25   8.123%   $75.9564   $75.96   $75.95   $76.00  
  Purchase #5 $242.31   3.245%   $250.173   $250.17   $250.15   $250.20  
  Purchase #6 $57.75   5.557%   $60.9592   $60.96   $60.95   $61.00  
  Purchase #7 $146.37   11.339%   $162.9669   $162.97   $162.95   $163.00  
  7 purchase totals = $954.29       $1,026.0222   $1,026.03   $1,026.00   $1,026.20